This invention relates to a mass spectrometer.
In general, a mass spectrometer includes an ionization part where a sample is ionized and an ion flow is generated, a beam converging part where the ions in this flow are converged and accelerated by means of a lens system comprising a plurality of plate electrodes or the like to generate an ion beam, and a detection part where the ions in this ion beam are separated according to the mass number (of the ratio between the mass m and the charge z) and the separated ions are analyzed.
Mass spectrometers of a so-called differential air discharge type are known as examples of mass spectrometers using an ionization method whereby a sample is ionized under an atmospheric condition (such as the atmospheric pressure ionization method). A mass spectrometer of the differential air discharge type is characterized as having its ionization part, beam converging part and detection part mutually separated by differential walls which need not necessarily be planar but are each provided with a passage, or a hole, with an extremely small diameter for allowing ions to pass therethrough. The beam converging part and the detection part are each provided with a pump for air discharge. During an analysis, the interior of the ionization part is maintained at an atmospheric pressure but these pumps are appropriately operated to such that the interior of the beam converging part is kept in a medium vacuum condition, say, at pressure about 10xe2x88x922 Pa and that of the detection part is kept in a high vacuum condition, say, at pressure about 10xe2x88x924 Pa.
Because a mass spectrometer of the differential air discharge type is of a relatively complicated structure with its interior separated by a plurality of partition walls, the maintenance work on its various internal components is generally cumbersome, and this problem is particularly significant regarding the beam converging part because the beam converging part according to the prior art technology is sandwiched between the ionization part and the detection part, being blocked thereby both from the front and from the back. According to the prior art technology, furthermore, an opening for the maintenance work through which the beam converging part can be accessed is provided on the front side of the spectrometer. Thus, components in the ionization part must be removed first in order to clear the access route for the beam converging part before components of the beam converging part can be accessed for their maintenance work.
Moreover, the beam converging part contains a large number of components such as the plate electrodes for the convergence and acceleration of the ion flow. In order to check all of these components, the operator must be able to make an access from all directions. As long as the beam converging part is inside the main body of the mass spectrometer, however, it is difficult to access these components from different directions. In reality, components of the beam converging part must be taken out of the main body of the spectrometer. Since no attempt has even been made to simplify the access to these components, it has been necessary to remove screws and bolts by using a screwdriver or the like as a cumbersome work process. It now goes without saying that the same processes must be repeated after the maintenance work has been completed in order to set the processed components back where they were. It also goes without saying that the same problem has existed with mass spectrometers of other types structured such that components for the beam convergence cannot be accessed from different directions.
It is therefore an object of this invention to provide a mass spectrometer structured such that components of its beam converging part such as a lens system can be easily maintained.
A mass spectrometer embodying this invention, with which the above and other objects can be accomplished, may be characterized not only comprising a lens system for generating an ion beam by converging and accelerating an ion flow obtained by ionizing a sample and an airtight main body which seals in this lens system but also wherein the lens system includes a lens unit having many components and there are also provided a positioning unit for properly positioning this lens unit inside the main body, elastic members contained inside the main body and holders for maintaining these elastic members in a deformed condition such that the lens unit is not only positioned by this positioning unit but also kept at this position by the elastic force of the elastic members supported by their holders.